Glutamate dehydrogenases (GDHs) are a broadly distributed group of enzymes that catalyse the reversible oxidative deamination of glutamate to ketoglutarate and ammonia [1]. The structure of GDH from Mycobacterium smegmatis revealed that it has a long N- and C-terminal segments flanking the catalytic core, comprising several domains. The flexible N-terminal domain comprises ACT-like and PAS-type domains which could act as metabolic sensors for allosteric regulation [2]. This is the first ACT-like domain (ACT1) found at the N-terminal of GDH. The ACT domains of these proteins differ from the archetypal ACT fold in that strand strand beta1 is located in the position usually occupied by strand beta4 creating an ACT-like topology with a beta1-4 antiparallel sheet [2].

1: A new class of glutamate dehydrogenases (GDH). Biochemical and genetic characterization of the first member, the AMP-requiring NAD-specific GDH of Streptomyces clavuligerus. Minambres B, Olivera ER, Jensen RA, Luengo JM; J Biol Chem 2000;275:39529-39542. PMID:10924516

2: 3D architecture and structural flexibility revealed in the subfamily of large glutamate dehydrogenases by a mycobacterial enzyme. Lazaro M, Melero R, Huet C, Lopez-Alonso JP, Delgado S, Dodu A, Bruch EM, Abriata LA, Alzari PM, Valle M, Lisa MN; Commun Biol. 2021;4:684. PMID:34083757